Production of hard dense bodies of vegetable fiber



Feb. 9, 1932. w. H. MASON 1,844,921

NNNNNN OR William H Mason Patented Feb. 9, 1932 UNITED STATES PATENT OFFICE WILLIA H. MASON, or LAUREL, MISSISSIPPI, AssIeNon 'ro MASCNITE CORPORATION,

01 LAUREL, MISSISSIPPI, A. CORPORATION OF DELAWARE PRODUCTION OF HARD DENSE BODIES F VEGETABLE FIBER Application filed May 4,

This invention relates to the production of bodies of hard dense material by subjecting a a mass of wet vegetable fibre or pulp to high pressure accompanied by heat until dry, the

1-; pressure being maintained preferably without diminution during the shrinking and drying of the material.

Such a process and product is disclosed in my Patents No. 1,663,505, granted March 20,

10,1928, and No. 1,767,539, granted June 24:,

In practicing the process of said patents. in the commercial production of large flat sheets or boards by means of a platen press,

I provide means for permitting escape of moisture in the form of Water and steam from the material under pressure by interposing a wire mesh screen between the material and the upper surface of the lower platen. Such screen forms a permanently roughened surface upon the material during the pressing and drying operation.

It is desirable that one of the surfaces of the pressed sheet or board should have a smooth finish entirely free from blemishes such as depressions, pits, and irregularities of various kinds.

In attempting to produce boards of this character, I have inserted between the lower surface of the upper platen and the material a surface plate made of highly polished steel provided with a very smooth layer of chromium formed by electrodeposition. the outer surface of such layer presenting the appearance of a highly polished surface. The use of such a surface plate has resulted in the production of finished boards having a highly polished surface. A considerable percentage of such boards. however, are found to have slight blemishes such as very shallow small depressions. The depth of suclra depression may be as little as .0005", yet by reason of the high degreeof polish of the surface, it is plainly visible to the eye when the light strikes the board obliquely.

The cause of such a blemish may be as follows: Let us assume that the web or sheet of Wet felted fibre which is to be pressed and is hereinafter referred to as a wet lap sheet) is not of perfectly uniform density or thick- 1931. Serial No. 534,772.

ness. As the surface plate contacts with the wet lap sheet, the soft material of the latter being pressed against the polished surface of the former acts as a gasket to entrap and hold air or water or steam which may collect in a pocket which is formed in the surface of the wet lap by reason of a slight surface irregularity or deficiency of material at that particular point or spot.

While such water is eventually converted to steam and the steam eventually escapes through the pores of the board, it has remained in such pocket long enough for the material to set so that there can be no filling of the pocket by flow of wet lap material from adjacent points of the sheet, and consequently the minute pocket or depression becomes permanent and visible in the finished board as previously described.

This invention has for its object the provision of a process and means by which the formation of such blemishes may be substantially prevented or avoided, and the per-- centage of perfectly finished boards greatly increased as compared with commercial production prior to the invention.

I have discovered that by suitably roughening the' pressing surface of the surface plate, so that it has a frosted appearance, I am able to produce finished sheets or boards having a smooth or polished surface and substantially all of which are free from blemishes of the class described.

The degree of roughening should be sufiiciently great to prevent the formation of the blemishes referred to. At its minimum, a polished board is produced, but the degree of polish is not so high as that produced by a polished surface plate. As the coarseness of the frosting is increased the board produced acquires a less polished, then a dull appearance which, however, is perfectly smooth to the touch and is suitable for many uses. The coarseness of the frosting may be increased to any desired degree, so long as the surface finish does not become undesirably rough.

Ordinarily a satisfactory degree of roughness of surface plate is obtained when the surface of the plate presents to the eye a frosted appearance and the fingers when moved will have a polished appearance, although not so highly polished as that produced by a 5 polished surface plate. At the maximum limit, the board surface will be dull but 'perfectly smooth to the sense of touch.

The surface of the board produced by a roughened or frosted surface plate is smoother than that of the plate for the reason that the pulp material of the wet lap sheet is not sufiiciently plastic to fill the minute depressions of the frosted surface. The bottom portions of these depressions remain void and a5 evidently prevent the wet lap forming an air or steam tight gasket against the surface plate, whereby air or steam is not entrapped and may find outlet from the pressed material by flowing through the depressions of the frosted surface of the surface plate, the result being the elimination of blemishes in the finished product.

In order that the invention may be more fully understood, reference is made to the accompanying drawing, of which Figure 1 is a vertical section of a portion of a wet lap sheet and a polished surface plate at the beginning of contact showing an undesirable pocket being formed in the wet lap, the depgh of such pocket being greatly exaggerate Fig. 2 is a similar view showing contact fully established between the wet lap sheet and surface plate; and

Fig. 3 is a vertical section, greatly enlarged, of a' portion of a surface plate constructed in accordance with my invention and a contacting wet lap sheet.

In Fig.1, 3 is a fragment of a wet lap sheet at the first moment of contact of its upper surface against a polished or unfrosted plate 4, showing a depression 5 which is about to form an air, water or steam pocket by reason of the gasket action of the surrounding wet lap material against the polished surface of the plate 4. Fig. 2 shows the contact of wet lap sheet and surface plate and pocket 5 fully established. Such pocket becomes permanent upon the setting of the material as it dries.

In order to avoid the formation of such blemishes, I provide a surface plate 6 having a roughened or frosted surface 7 as in Fig. 3.

The depressions of the surface 1 are of such depth and narrowness that the material of the wet lap does not reach the bottom thereof and does not cooperate with the surface 7 to form a gasket to entrap air, water, or steam.

The surface plate 6 may be made of any desired metal (which term includes metal alloys) and the frosted surface may be produced by etching, electrodeposition, sand blast, or other method. 4

I have obtained very favorable results by the use of a steel plate of approximately thickness upon which a layer of chromium is lated by electrodeposition.

t is possible by an electroplating process to de osit either a highly polished or a suitably rosted film or layer of chromium. The

former is obtained by the use ofa warm bath' and a low current density, and should be avoided. The frosted coatingmay be obtained by electroplating from a cold bath by means of a current of high density or concentration, as for example: the plating may be done at a temperature of 28 C. having a current density of approximately 1.4 amperes per square inch.v The plating may be done in a bath made up in approximately the following conditions: 34 oz. chromic acid per gallon of water. To this is added about oz. of sulphuric acid to the gallon.

After having obtained a suitable surface plate, the same may be used in the manner described for a considerable length of time. Eventually, the surface of such plate becomes smoothed out by the pressing operations to which it is subjected, so that it loses its frosted appearance and appears smooth. It may then be reconditioned y connecting it as an anode in the plating bath for a short time to clean it and then connecting it as a cathode and plating it in the same way as before.

In order to produce a hard board of the character described, pressures of from 200 lbs. to 700 lbs. per, square inch give ver satisfactory results in producing a bar dense product, but variations in pressure above and below these amounts may be resorted to, if desired. The pressure upon the material should be maintained until it is completely dry. The pressure used ordinarily results in a product having a specific gravity of approximately one or more than one. The temperature of the platens should be above 212 Fahrenheit, and may range to such higher value as will dry the material without overheating or charring it. For example, steam at a pressure of the order of lbs. to 200 lbs. per square inch may be used with good results for heating the platens. I

I claim:

1. A pressing member having a flat extended pressing surface of frosted metal.

2. A pressing member having a flat extended pressing surface of frosted chromium.

3. A pressing member for the hot press drying of a wet mass of vegetable fiber, said member having an extended pressing surface of frosted metal and such frosting being sufficiently fine to produce a surface smooth to the touch and sight, and sufficiently coarse to minimize the formation of pockets in the surface of the material pressed.

4. A pressing member for the hot press drying of a Wet mass of vegetable fiber, said member having an extended pressing surface of frosted chromium and such frosting being. sufliciently fine to produce a surface smooth to the touch and sight, and sufficient- 1y coarse to minimize the formation of pockets in the surface of the material pressed. In testimony whereof, I have signed my name hereto. 7

WILLIAM H. MASON. 

